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Aquaponics: When Growbeds Get Old – Sh*t Happens

Years ago there was an old expression applied to computer industry surrounding software programming – “Garbage in – Garbage out!”
That expression of what goes around, comes around can equally be applied to aquaponics and the biofiltration mechanism that keeps the whole system flourishing along nicely – the growbeds.
The filter system where the billions of bacteria survive can eventually get clogged up with fish solids and “dead zones” appear that turn the system nasty and unfriendly to growing plants or fish.

The question was how long will it take for the fish solid waste – the sh*t to build up to the point where some maintenance was needed and the system filter material the clay beads or hydroton or stone gravel media would eventually need to be taken out, replaced or cleaned?

Profile of a 5 year old gravel grow bed that has reached the end of its life

It was generally thought that the amount of fish solids and waste build up without any supplementary solids filtration would take around 18 months depending on fish load and growbed size and so on.
But with the introduction of compost worms that period for many aquaponics enthusiasts seemed to extend the life of the system and go on from one year to the next.

Worms are efficient to a certain extent but they are not the entire solution. The eventual question amongst members was how long before the system would crash and fail?

“How can it be run dry when it is submersed in the fish tank????” he shouted with colourful adjectives.”

Maintenance
Every year was another milestone for Murray Hallam who builds some of the best Grow Beds in Australia from durable 300mm deep fiberglass.
His troughs are large solid and deep constructions and seemed to go on from one year to another without maintenance.
Many people felt that aquaponics system once running correctly were bullet proof and no maintenance was needed. But this is not true as Murray was the first to admit.

“Maintenance is required right through a well run an aquaponics system.” said Murray, “For example, we had a client return a pump that had clearly been run “dry” and was badly damaged. Became agitated when it was suggested that the pump had been run dry. “How can it be run dry when it is submersed in the fish tank????” he shouted with colourful adjectives.

“Easy really, the pump filter screen had never been cleaned, therefore the underwater pump was getting next to no water flow and in effect running dry. Terminal damage to the pump was only a matter of time.” Same principle applies to the growbed.

Fish poop and muck from 5 years of service

Anaerobic Dead Zones

Anaerobic bacteria begin to colonise parts of your growbed in areas where oxygen is not being delivered. The good aerobic bacteria are replaced with the other sort. A good tell tale sign is the pH will give you warning signals. Instead of creeping up gradually becoming more acid as it does in a healthy aerobic system, the pH drift will halt and reverse and become more alkaline.

This is what happened in Murray’s five year old growbed system.

“This particular system has, over the last few months started to show a slight rise in pH instead of the typical slow drop,” said Murray, “which is a pretty good indicator of anaerobic areas in the system somewhere. I suspect one or two “dead” areas in this bed.”

The solution was to dig out the media and wash it. Murray decided to replace the entire gravel media and use this old media to fill in pot holes in his driveway! Nutrient rich potholes!

Lee Sykes levels new gravel into the old bed

Replacing the Gravel
Three quarter inch gravel was used to replace the media in this old bed. “The new gravel was shoveled in and leveled, then the water turned back on to start the fill and drain cycle via the auto siphon.” said Murray.

Altogether about two hours work for Murray and his assistant Lee to replace the gravel. This new bed will take a number of weeks for the bacteria to reestablish and begin another 5 years of productive service producing an endless supply of vegetables and fish.

According to Murray, “Nothing is “self sustaining” or maintenance free in this world.”

“Everything requires some work and if I really have to dig up a (grow) bed once every 5 years, I reckon that is darn good.” he said.

“What other gardening method can give 5 years clear service of just planting and harvesting?”

6 Comments

Jul01

Matt

I bet that gravel could be cleaned by tumbling it in a cement mixer and using a hose to rinse out the loosened soil. Porus clay could be made porous again with concentrated hydrogen peroxide, which bleaches organic materials with oxygen, and leaves no toxic residue.

Always such a wealth of information to be had on your site Frank, thank you. I am wondering if the same can be said for those of us using hydroton, perhaps things would get to this state much quicker, thoughts?

Hydroton has more places for things to get trapped, but then since the media tends to become lighter as water fills the bed, perhaps the solids dislodge easier flowing though the bed easier…

Thank you for your comments Shaun. Thats a good question. We’ve had our system running for over 2 years. 100% Hydroton. We will know the answer to that question soon I think but so far everything is still running well. Yes root mass can squeeze hydroton. I have a great photo which would make a good post that shows the power of dense root mass in aquaponics and hydroton. Thank you for the idea 🙂